The Elasto-Gel Cervical Collar Wrap allows maximum conformity, heat transfer and comfort. Use hot or cold; retains temperature for 20-30 minutes. Made from flexible Elasto-Gel. Velcro closure for easy positioning. May be heated and/or cooled repeatedly. Stays soft and flexible. Heat in microwave or in conventional oven. Cool in freezer. Difference between Polycotton and Lyca Cover: The Polycotton and Lycra covers look identical and are the exact same gel. The cover is substantially different. Lycra cover has a 4 way stretch lycra with a loop back so that the velcro strap will stick anywhere on the collar, making it a custom fit. Also, lycra gives better hot and cold transfer than any material on the market. The polycotton cover is a two way stretch cotton cover, the lycra is a 4 way stretch lycra (makes it easier to get the cover off for washing) The polycotton cover has a small patch of the velcro like hook on it and that is the only place where you can place the velcro strap to make it hold the collar in place. Elasto-Gel Therapy Products are designed to provide moist heat therapy or soothing cold therapy for relief of minor muscular and joint aches and pains. The hot or cold therapy will last 20 to 40 minutes per application. The product is held in place with hook and loop type closures, which allow the user to move about during therapy. The product is microwavable so it can provide nearly continuous heat therapy. When used cold, the product conforms to contours, even at -20F (-30C), allowing comfortable soothing cold applications.